The method for fine comminution is known for example from DE-B-27 08 053. In order to carry out this method so-called material bed roll mills may be considered which consist of two rolls which are pressed against one another with high pressure and are driven in opposite directions.
However, the efficiency of these roll mills is limited by the fact that the grinding tools, i.e. the rolls, have to transport the mill feed material into the pressing zone. In this case the "transport speed" is highly dependent upon the friction conditions of the as yet unpressed granular mass of material on the roll surface and upon how stable the material bed is in order to transfer the pressure. Thus the mill feed material is drawn into the grinding gap by the roll surfaces. The actual pressing begins at an angle of nip which is set automatically. The pressing speed at the beginning of the compression stress may be calculated on the basis of the peripheral speed of the grinding rolls. The pressing speed is understood here to mean the speed at which the distance between two opposing points on the surface of the two rolls is decreased.
The pressing speed at the start of the compression stress is in direct relation to the throughput of the roll mill. An increase in the efficiency of such mills is possible through an increase in the peripheral roll speed only in so far as the material feed through the roll transport before the pressing can keep pace with the pull-through speed in the pressing zone at the desired pressing density. Otherwise an interruption of the material flow is to be expected and the consequence is a high instability of the pressing operation. For this reason roll mills can only be operated at initial pressing speeds of about 0.5 m/s.
The object of the invention, therefore, is to improve the known method in such a way that the throughput is increased.